A strict effluent regulation is imposed on metal contained in industrial drainage water, such as mercury, cadmium, copper, and zinc which are hazardous to the human body. Accordingly, further improved treatment effects are required. In recent years, the demand for metal resources is also increasing. In particular, rare metal and noble metal are used as essential materials in various areas such as semiconductor lasers and battery materials. Since the reserve and supply amount of such metal are limited, it is desired to recover metal from waste substances and waste liquids.
Under such circumstances, it is attempted to adsorb and remove metal ions by treating drainage water with a chelate resin. Since the ability to form a complex with metal ions varies depending on the functional group structure of the chelate resin, chelate resins having an iminodiacetic acid group, a polyamine group, an amino phosphate group, an isothionium group, a dithiocarbamic acid group, a glucamine group, and the like are commercially available. Among these, an iminodiacetic acid group, which has the ability to form a complex with various metals, is widely utilized. For example, Patent Literature 1 describes that an iminodiacetic acid is introduced into a chelate resin having polyethyleneimine on the surface, thereby to further strengthen the chelate effects. Patent Literature 2 discloses a chelate resin in which an iminodiacetic acid and an amino group are introduced into and bonded to a resin carrier. Patent Literature 3 discloses a metal adsorbent in which a primary amino group of a polyamine-based macromolecule is N-carboxymethylated to become an iminodiacetic acid group in a macromolecule-fixed type metal adsorbing material in which a polyamine-based macromolecule is fixed to an insoluble carrier. Patent Literature 4 discloses a chelator which has a functional group selected from an iminodiacetic acid, an N-methyl-D-glucamine, and polyethyleneimine. Patent Literature 5 discloses a chelating agent of a polyethylene iminodiacetic acid.
However, the fact is that a general-purpose chelate resin having an iminodiacetic acid group does not necessarily have satisfactory adsorption effects. To address this concern, there is a demand for a chelate resin which can be easily and efficiently produced and can efficiently adsorb and separate metal ions, compared to a known chelate resin having an iminodiacetic acid group which is used for adsorbing metal ions.                Patent Literature 1: Japanese Patent Application Laid-Open No. 2005-21883        Patent Literature 2: Japanese Patent Application Laid-Open No. 2006-328203        Patent Literature 3: Japanese Patent Application Laid-Open No. 2011-88047        Patent Literature 4: Japanese Patent Application Laid-Open No. 2005-2414        Patent Literature 5: International Publication No. W02007-127587        